1. Field of the Invention
The present invention relates to a polytetrafluoroethylene-containing powder mixture containing polytetrafluoroethylene particles with a particle size 10 .mu.m or smaller (A) and organic polymer particles (B), to a thermoplastic resin composition including the mixture and to molded articles made therefrom.
2. Description of the Related Art
Polytetrafluoroethylene (PTFE) has excellent heat resistance, chemical resistance and electrical insulating properties and is widely used as a coating material because of its special surface characteristics including water and oil repellent, non-adhesive and self-lubricating properties. Also, its high crystallinity and low intramolecular force give it a nature suitable to forming fibers with only minimal stress, and when combined with thermoplastic resins it is possible to achieve better molding workability and mechanical properties, allowing it to be used as an additive for thermoplastic resins.
Japanese Unexamined Patent Publications No. 5-214184 and No. 6-306212, for example, disclose resin compositions wherein polytetrafluoroethylene is combined with polyolefins. Also, Japanese Unexamined Patent Publication No. 7-324147 discloses a process for producing polyolefin-based resin compositions whereby polytetrafluoroethylene prepared by mixing polytetrafluoroethylene with a powdered dispersion medium under high shear action is first made into fibers and then mixed with a polyolefin.
A drawback exists, however, in that polytetrafluoroethylene has poor dispersibility in common thermoplastic resins which contain no halogen atoms, and fails to uniformly disperse with only simple blends as described in Japanese Unexamined Patent Publications No. 5-214184 and No. 6-306212, thus notably impairing the surface appearance of resulting molds.
Furthermore, it is difficult to convert all of the polytetrafluoroethylene to fibers with shearing force by the process described in Japanese Unexamined Patent Publication No. 7-324147, and even the polytetrafluoroethylene fibers aggregate in the matrix resin making it impossible to obtain a uniform composition.
In other words, the dispersibility of polytetrafluoroethylene in matrix resins constitutes a problem in all of these processes, and therefore large amounts of the polytetrafluoroethylene have been necessary in order to exhibit the aforementioned useful properties.